www-apps/cgit: fix missing group on installation

www-apps/cgit: fix missing group on installation

After a recent change in user.eclass, this package no longer creates
the required group that's used later in src_install.  I've adjusted the
ebuilds to restore the original behavior as intended before this eclass
change.

https://gitweb.gentoo.org/repo/gentoo.git/commit/eclass/user.eclass?id=3afc0d7b8b5e90c50d66c5a845b96c33e521e6e8
Closes: https://bugs.gentoo.org/688890
Package-Manager: Portage-2.3.76, Repoman-2.3.17
RepoMan-Options: --force
Signed-off-by: Ben Kohler <bkohler@gentoo.org>